Methods and systems relating to optical networks

ABSTRACT

Data center interconnections, which encompass WCs as well as traditional data centers, have become both a bottleneck and a cost/power issue for cloud computing providers, cloud service providers and the users of the cloud generally. Fiber optic technologies already play critical roles in data center operations and will increasingly in the future. The goal is to move data as fast as possible with the lowest latency with the lowest cost and the smallest space consumption on the server blade and throughout the network. Accordingly, it would be beneficial for new fiber optic interconnection architectures to address the traditional hierarchal time-division multiplexed (TDM) routing and interconnection and provide reduced latency, increased flexibility, lower cost, lower power consumption, and provide interconnections exploiting N×M×D Gbps photonic interconnects wherein N channels are provided each carrying M wavelength division signals at D Gbps.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority as divisional patentapplication of U.S. patent application Ser. No. 15/114,479 filed Sep. 8,2016 entitled “Methods and Systems Relating to Optical Networks”, whichitself claims the benefit of priority as a 371 National. Phaseapplication of PCT/CA2015/000,139 filed Mar. 10, 2015 entitled “OpticalDevice with Tunable Optical Wavelength Selective Circuit”, which itselfclaim the benefit of priority from U.S. Provisional Patent Application61/950,238 filed Mar. 10, 2014 entitled “Methods and Systems Relating toOptical Networks”, the entire contents of each being herein incorporatedby reference.

FIELD OF THE INVENTION

This invention relates to optical networks and more particularly towavelength division multiplexed networks for data center and cloudcomputing applications.

BACKGROUND OF THE INVENTION

Cloud computing is a phrase used to describe a variety of computingconcepts that involve a large number of computers connected through areal-time communication network such as the Internet, see for exampleCarroll et al in “Securing Virtual and Cloud Environments” (CloudComputing and Services Science, Service Science: Research andInnovations in the Service Economy, Springer Science Business Media,2012). It is very similar to the concept of utility computing. Inscience, cloud computing is a synonym for distributed computing over anetwork, and means the ability to run a program or application on manyconnected computers at the same time.

In common usage, the term “the cloud” is essentially a metaphor for theInternet, see for examplehttp://www.netlingo.com/word/cloud-computing.php. Marketers have furtherpopularized the phrase “in the cloud” to refer to software, platformsand infrastructure that are sold “as a service”, i.e. remotely throughthe Internet. Typically, the seller has actual energy-consuming serverswhich host products and services from a remote location, so end-usersdon't have to; they can simply log on to the network without installinganything. The major models of cloud computing service are known assoftware as a service, platform as a service, and infrastructure as aservice. These cloud services may be offered in a public private orhybrid network. Today, Google, Amazon, Oracle Cloud, Salesforce, Zohoand Microsoft Azure are some of the better known cloud vendors. Whilstcloud computing can be everything from applications to data centers acommon theme is the pay-for-use basis.

The major cloud vendors provide their services through their own datacenters whilst other third party providers access either these datacenters or others distributed worldwide to store and distribute the dataon the Internet as well as process this data. Considering just Internetdata then with an estimated 100 billion plus web pages on over 100million websites, data centers contain a lot of data. With almost twobillion users accessing all these websites, including a growing amountof high bandwidth video, it's easy to understand but hard to comprehendhow much data is being uploaded and downloaded every second on theInternet. At present the compound annual growth rate (CAGR) for globalIP traffic between users is between 40% based upon CiSCo's analysis (seehttp://www.cisco.com/en/US/solutions/collateral/ns341/ns525/ns537/ns705/ns827/white_paper_c11481360_ns827_Networking_Solutions_White_Paper.html) and 50% based upon the University of Minnesota's MinnesotaInternet Traffic Studies (MINTS) analysis. By 2016 this user traffic isexpected to exceed 100 exabytes per month, over 100,000,000 terabytesper month, or over 42,000 gigabytes per second. However, peak demandwill be considerably higher with projections of over 600 million usersstreaming Internet high-definition video simultaneously at peak times.

All of this data will flow to and from users via data centers andaccordingly between data centers and within data centers so that theseIP traffic flows must be multiplied many times to establish total IPtraffic flows. Data centers are filled with tall racks of electronicssurrounded by cable racks where data is typically stored on big, fasthard drives. Servers are computers that take requests to retrieve,process, or send data and access it using fast switches to access theright hard drives. Routers connect the servers to the Internet. At thesame time these data centers individually and together providehomogenous interconnected computing infrastructures. When hosted inmassive data centers these are also known as warehouse scale computers(WSC) which provide ubiquitous interconnected platforms as a sharedresource for many distributed services.

At the same time as requiring a cost-effective yet scalable way ofinterconnecting data centers and WSCs internally and to each other mostdatacenter and WSC applications are provided free of charge such thatthe operators of this infrastructure are faced not only with thechallenge of meeting exponentially increasing demands for bandwidthwithout dramatically increasing the cost and power of theirinfrastructure. At the same time consumers' expectations ofdownload/upload speeds and latency in accessing content provideadditional pressure.

Accordingly data center interconnections, wherein we encompass WSCs aswell as traditional data centers within the term data center, havebecome both a bottleneck and a cost/power issue. Fiber optictechnologies already play critical roles in data center operations andwill increasingly. The goal is to move data as fast as possible with thelowest latency with the lowest cost and the smallest space consumptionon the server blade and throughout the network.

According to Facebook™, see for example Farrington et al in “Facebook'sData Center Network Architecture” (IEEE Optical InterconnectsConference, 2013 available athttp://nathanfarrington.com/presentations/facebook-optics-oida13-slides.pptx),there can be as high as a 1000:1 ratio between intra-data center trafficto external traffic over the Internet based on a single simple request.Within data center's 90% of the traffic inside data centers isintra-cluster. Further, Farrington notes that whilst a Folded Clostopology provides the best economics at the largest scales the cablingcomplexity is a daunting problem as it is quadratic function of thenumber of nodes. Farrington notes that the issue of reducing the cablingcomplexity of Folded Clos topologies is an industry-wide problem worthsolving.

Accordingly, it would be beneficial for new fiber optic interconnectionarchitectures to address the traditional hierarchal time-divisionmultiplexed (TDM) routing and interconnection and provide reducedlatency, increased flexibility, lower cost, lower power consumption, andprovide interconnections exploiting N×M×D Gbps photonic interconnectswherein N channels are provided each carrying M wavelength divisionsignals at D Gbps.

Other aspects and features of the present invention will become apparentto those ordinarily skilled in the art upon review of the followingdescription of specific embodiments of the invention in conjunction withthe accompanying figures.

SUMMARY OF THE INVENTION

It, is an object of the present invention to mitigate limitations in theprior art relating to optical networks and more particularly towavelength division multiplexed networks for data center and cloudcomputing applications.

In accordance with an embodiment of the invention there is provided adevice comprising:

-   a pluggable optic housing;-   a pair of optical connectors or pigtails coupled to a receiver and a    transmitter position allowing the daisy-chaining of multiple    instances of the device as well as point to point connectivity    between two instances of the device onto two fibers; and-   a tunable optical wavelength selective circuit comprising a    plurality of wavelength selective filters and a rotatable    microoptoelectromechanical system (MOEMS) for selecting a wavelength    selective filter of the plurality of wavelength selective filters to    tune the tunable optical wavelength selective circuit.

In accordance with an embodiment of the invention there is provided anetwork comprising a plurality of ROADM nodes where each ROADM node iscapable of tuning to the same channel thereby enabling a wavelength or agroup of wavelengths to be broadcast to the one or more ROADM nodes byconfiguring a tunable optical wavelength selective circuit within a nodeto tune to the same wavelength or group of wavelengths as anothertunable optical wavelength selective circuit within a daisy chain oftunable optical wavelength selective circuits forming the plurality ofROADMs.

In accordance with an embodiment of the invention there is provided anetwork comprising a plurality of serially connected reconfigurableoptical add-drop multiplexers (ROADMs), each ROADM providing for theaddition of a first predetermined number of wavelength channels to alink within an optical network to which the ROADMs are connected and thesubtraction of a second predetermined number of wavelength channels fromthe link of the optical network to which the ROADM is connected, whereineach ROADM is configured upon determination of its position within theplurality of serially connected ROADMs.

In accordance with an embodiment of the invention there is provided anetwork comprising a plurality of nodes, each node, of the plurality ofnodes being connected to N−1 subsequent sequential nodes via awavelength division multiplexed link comprising at least M wavelengths,wherein each node of the plurality of nodes is connected to the nextN^(th) node via the N^(th) wavelength of the at least M wavelengths.

In accordance with an embodiment of the invention there is provided asystem comprising:

-   a MEMS based latching 1×N optical switch;-   M optical sources, each optical source operating within a    predetermined wavelength range;-   at least one optical time domain reflectometry (OTDR) signal;-   M optical couplers, each optical coupler to overlay an OTDR signal    to the M optical sources to a predetermined output of the N outputs    of the 1×N optical switch; and-   a controller for determining whether to change the state of the MEMS    based latching 1×N optical switch in dependence upon at least the    OTDR signals from the M optical sources.

In accordance with an embodiment of the invention there is provided adevice comprising:

-   a transceiver body, the body having an external physical geometry    compliant to a predetermined optical transceiver standard-   a MEMS based latching 1×N optical switch;-   a micro-controller integrated in the transceiver body for    controlling the 1×N optical switch; wherein-   the input of the 1×N optical switch is for coupling to a first    optical transceiver via at least one of a connectorised interface on    the device and a fiber pigtail;-   the N outputs of the 1×N optical switch are for coupling to N second    optical transceivers via at least one of connectorised interfaces on    the device and fiber pigtails.

In accordance with an embodiment of the invention there is provided adevice comprising:

-   a transceiver body, the body having an external physical geometry    compliant to a predetermined optical transceiver standard;-   a reconfigurable optical add-drop switch employing a plurality of    tunable optical wavelength selective circuits, each tunable optical    wavelength selective circuit comprising a plurality of wavelength    selective filters and a rotatable microoptoelectrormechanical system    (MOEMS) for selecting a wavelength selective filter of the plurality    of wavelength selective filters to tune the tunable optical    wavelength selective circuit; and-   an optical amplifier; wherein-   the reconfigurable optical add-drop switch and optical amplifier are    packaged within the transceiver body.

In accordance with an embodiment of the invention there is provided adevice comprising:

-   a polarization independent amplifier comprising:-   a polarization splitter to split an incoming optical signal into TE    and TM polarization components;-   a polarization rotator to rotate the TM polarization to TE;-   a pair of semiconductor optical amplifiers to amplify the pair of TE    optical signals; and-   a combiner to combine the pair of outputs from the pair of    semiconductor optical amplifiers; and-   a reconfigurable optical add-drop module for dropping and adding a    predetermined band of wavelengths from a plurality of bands of    optical wavelengths.

Other aspects and features of the present invention will become apparentto those ordinarily skilled in the art upon review of the followingdescription of specific embodiments of the invention in conjunction withthe accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described, by way ofexample only, with reference to the attached Figures, wherein:

FIG. 1 depicts data center network connections according to the priorart;

FIG. 2 depicts a two-tier leaf spine architecture according to the priorart with limited scaling, out;

FIG. 3 depicts a two-tier leaf spine architecture according to anembodiment of the invention supporting scaling out;

FIG. 4 depicts a two-tier leaf spine architecture according to anembodiment of the invention;

FIG. 5 depicts an interconnection diagram for multiple leaf switch saccording to an embodiment of the invention;

FIG. 6 depicts a reconfigurable add-drop multiplexer (ROADM) exploitingMEMS based wavelength tunable devices according to an embodiment of theinvention;

FIG. 7 depicts wavelength settable optical components exploiting MEMSmirror elements in conjunction with wavelength selective reflectingelements;

FIG. 8 depicts the ROADM according to the architecture of FIG. 6implemented using the wavelength settable optical components depicted inFIG. 7;

FIG. 9 depicts a chordal interconnection pattern for a single nodewithin a ring network according to an embodiment of the invention;

FIG. 10 depicts a chordal interconnection pattern for a ring networkaccording to an embodiment of the invention with multiple nodespopulated;

FIG. 11A depicts a remote note to central office interconnectionexploiting embedded OTDR in conjunction with latching 1×2 protectionswitching;

FIG. 11B depicts OTDR and latching 1×2 MEMS protection switchingexploiting SFP pluggable modules and out of band serial communicationsaccording to embodiments of the invention;

FIG. 12 depicts a central office to remote location interconnectionusing C+L bands wherein Bragg gratings embedded into connectingpatchcords provided for coloured transmitters based upon colourlesstransceivers according to an embodiment of the invention;

FIGS. 13 and 14 depict bidirectional link connectors with embedded Bragggratings and/or C+L band filters according to embodiments of theinvention;

FIGS. 15A, 15B, 16A and 16B depict optical receivers exploiting MEMSmirror elements in conjunction with wavelength selective reflecting andtransmissive elements respectively;

FIG. 17 depicts an optical transmitter exploiting MEMS mirror element inconjunction with wavelength selective reflecting elements in siliconwith integrated semiconductor die containing an optical gain block, ahigh reflectivity mirror, and external modulator;

FIG. 18 depicts a transceiver employing transmitter and receiver,optical sub-assemblies according to an embodiment of the inventionexploiting MEMS mirror elements in conjunction with wavelength selectiveelements;

FIG. 19 depicts a transceiver employing a single silicon circuitcomprising transmitter and receiver optical sub-assemblies according toan embodiment of the invention exploiting MEMS mirror elements inconjunction with wavelength selective elements;

FIG. 20 depicts a transceiver employing a single silicon circuitcomprising transmitter and receiver optical sub-assemblies according toan embodiment of the invention exploiting MEMS mirror elements inconjunction with wavelength selective elements together with a C+Lfilter;

FIG. 21 depicts a sub-band reuse plan for unicast communication goingfrom leaf to spine between two leaves within a leaf-spine network suchas depicted in FIG. 4 according to an embodiment of the invention;

FIG. 22 depicts an interconnection diagram for two ReconfigurableOptical Add/Drop Switch Transceiver with Electronic Regeneration(ROADSTER) network rings using a contention less, direction less,colorless optical switch whilst providing filter less and colorless SOAoverlay amplification to a DP-16QAM network via the pass-throughfunctionality of the polarization less SOA included in ROADSTERaccording to an embodiment of the invention;

FIG. 23 depicts a protected leaf spine on the same ring by using twodifferent fiber in two independent ROADSTER network ring according to anembodiment of the invention;

FIG. 24 depicts a multicast scenario for a leaf-spine network such asdepicted in FIG. 4 according to an embodiment of the invention; and

FIGS. 25 and 26 depict 4×4 and 8×8 optical switch matrices according toembodiments of the invention employing 1×4 and 1×8 MOTUS optical enginesand directional couples for enhanced layout and reduced cross-overswhilst FIG. 27 depicts an optical waveguide cross-over according to anembodiment of the invention exploited within the 4×4 and 8×8 opticalswitch matrices depicted in FIGS. 25 and 26.

DETAILED DESCRIPTION

The present invention is directed to optical networks and moreparticularly to wavelength division multiplexed networks for data centerand cloud computing applications.

The ensuing description provides exemplary embodiment(s) only, and isnot intended to limit the scope, applicability or configuration of thedisclosure. Rather, the ensuing description of the exemplaryembodiment(s) will provide those skilled in the art with an enablingdescription for implementing an exemplary embodiment. It beingunderstood that various changes may be made in the function andarrangement of elements without departing from the spirit and scope asset forth in the appended claims.

1. Optical Leaf/Spline Switch Architectures Exploiting Roam Transceivers

1A: Introduction

According to the North Bridge Venture Partners Future of Cloud ComputingThird Annual 2013 Survey(http://www.northbridge.com/2013-cloud-computing-survey), the cloud wasexpected to reduce complexity, but experience has demonstrated theopposite. More than half (55.1%) of the respondents to the survey haveindicated that hybrid/multi-cloud providers will likely benefit from thebiggest growth opportunities over the next few years, as they are bestpositioned to ease the cloud complexity problem. A combination of aPublic and a Private cloud forms a Hybrid Cloud. The combination ofmultiple Public Cloud services forms a Multi-Cloud. The combination of aHybrid Cloud and a Multi-Cloud forms a Hybrid/Multi-Cloud (hereinafterreferred to as an HM cloud).

It thus follows that the most successful datacenters will be those whowill both connect multiple cloud providers to hosted enterprise privatecloud infrastructures as well as facilitate seamless extensions of HMclouds all the way to the enterprise premise(s). With HM clouds,enterprises will now be able to switch more rapidly between providers ofa specific application domain.

Historically, datacenter interconnections for a given customer took theform of a few cross-connects measuring tens of meters within a singledatacenter. As needs have arisen for resilient hyperscale datacenters,cross-connects have increased to several hundreds of meters within thedatacenter and have been extended to several tens of kilometers acrossdatacenters within the same metropolitan market. Accordingly, newfunctionalities are required in datacom networks in order to enable thecapabilities that are sought for by HM Cloud datacenter customers.

Accordingly, the inventors through embodiments of the invention areextending and adapting Wavelength Division Multiplexing for use withinintra and inter data center applications allowing data center operatorsto truly scale out HM clouds. In parallel through World PatentApplication PCT/CA2013/000086 filed Jan. 30, 2013 entitled “Method,Topology and Point of Presence Equipment for Serving a Plurality ofUsers via a Multiplex Module”, the authors have described how toleverage the passive multipoint capabilities inherent to WDM-PONtechnology to allow for the future proofing, of the underlyinginfrastructure for Software Defined Networking (SDN) and NetworkFunctions Virtualization (NFV).

At the same time as supporting increased data flow, increased customerexpectations and lower costs, no compromises can be made on thereliability of cloud computing communications that occur inside thedatacenter, between datacenters and in the access of datacenters. Toachieve what may be considered telecommunications grade resiliencyrequirements then cloud computing vendors need to consider issues suchas geographic failover and load balancing across multiple datacenterfacilities within a given metro market.

It thus follows that the most successful datacenters will be those whowill also host seamlessly interconnected services from multiple diversefacilities within the same metropolitan market. In the past, it wassufficient to interconnect the datacenter hosted enterprise cloudinfrastructure with the one on its premises. However, HM clouds requiremultipoint connectivity with many more degrees of interconnection toallow multiple cloud providers to reach both the datacenter hosted andthe on premise enterprise private datacenter. Further, WDM-PONTechnology enables links capable interconnecting HM Clouds acrossmultiple datacenters that can be several kilometers apart.

Passive multipoint connectivity enabled by dense wavelength divisionmultiplexing (DWDM) provides a future-proof upgrade path to extract morevalue out of existing fiber optic access networks. For example, WDM-PONtechnology enables 40 circuits of 10 Gbps to share a single opticalfiber over unamplified distances of up to 40 kilometers. At the sametime a single pair of optical fiber via WDM-PON also enables the passivemultipoint steering to 40 different destinations within the outsideplant.

Fiber optic network operators are now seeking to consolidate multiplesmaller points of presence into larger datacenters in order to reducetheir operational expenditures. WDM-PON Technology enables a similarsplit ratio than network based on power splitters such as EPON or GPON,but with the advantage of 50% less attenuation. A strong business casenow supports the use of WDM-PON technology in the outside plant as ahigh-performance onramp to HM clouds. The use of WDM-PON technology foraccessing datacenters then creates an opportunity for considering itsuse much deeper within the datacenter infrastructure to overcomelimitations in current approaches to datacenter networking.

1B: Current State of the Art Without DWDM Technology in Intra-DataCenter Communications

1B.1: Managing Oversubscription to Control Costs in Two-Tier Leaf-SpineArchitectures

The majority of hyperscale datacenters networks today are designedaround a two-tier leaf/spine Ethernet aggregation topology leveragingvery high-density switches such as depicted in FIG. 1. Within thistwo-tier leaf/spine topology the oversubscription ratio is the ratio ofdownlink ports to uplink ports when all ports are of equal speed. With10 Gbps server interfaces, and considering these as part of a 3:1oversubscribed architecture, then 40 Gbps of uplink bandwidth to thespine switches is necessary for every 12 servers. The 3:1 thresholdtoday being generally seen as a maximum allowable level ofoversubscription and is carefully understood and managed by thedatacenter operators. Accordingly, a 3:1 oversubscribed leaf/spine/corearchitecture supporting communications within and between a pair of datacentres, Data Centre A 110 and Data Centre 120 generally consists ofservers 130 interconnected at 10 Gbps to Top of Rack (ToR) Ethernetswitches that act as first level aggregation, the leaf switches 140.These ToR leaf switches 140 then uplink at 40 Gbps into end of row (EoR)Ethernet switches, which act as the spine switches 150 of the leaf/spinetopology. As an example, with a 48-port ToR switch of 10 Gbps per port,ensuring a maximum 3:1 oversubscription ratio requires that the ToRswitches have 16 uplink ports at 10 Gbps or alternatively, 4 ports at 40Gbps. Then in order to enable connectivity across datacenters, the spineswitches then connect at 100 Gbps to core routers 160, which then inturn interconnect to optical core infrastructure made up metro/long-haulDWDM/ROADMs transport platforms.

1B.2: Achieving Non-Blocking Connectivity in Two-Tier Leaf/SpineArchitectures

In FIG. 2 the two-tier leaf spine architecture cannot scale out to add amaximum amount of servers within the chosen oversubscription parameterand at a constant latency. As depicted from the leaf a 40 Gbps uplink ismade to a single spine switch, Spine #1, which therefore reduces thenumber of spine switches accessed such that some connections, e.g. Spine#N. Accordingly, the bisection bandwidth is affected and hence fewerleaf switches and thence fewer servers are connected. In contrast inFIG. 3, in a two-tier leaf/spine architecture according to an embodimentof the invention then it only scale out to add a maximum amount ofservers within the chosen oversubscription parameter and at a constantlatency, because every leaf switch is connected to every spine switch.Accordingly, to achieve this and scale out, the bandwidth of leaf switchuplinks at 40 Gbps is instead broken out as 4 links of 10 Gbps that arethen connected to 4 distinct spine switches. Hence, more uplinks connectto more spines and thence more leaf switches and servers can besupported.

1C.1 Ring Network Leaf-Spine Connectivity exploiting ReconfigurableOptical Add-Drop Multiplexer

Using dense wavelength division multiplexing (DWDM) in conjunction withsub-band aggregation and an optical device that can tune a wavelength ora sub-band for both the transmission and reception side offers a noveldatacenter interconnectivity methodology. Accordingly, embodiments ofthe invention allow for a reduction in the count of optical fiber links,the length of the optical fibers and also lower the number of requiredpositions for connectivity.

Multiple nodes could also tune a reception wavelength or a sub-bandaltogether and provide multicast capabilities to multiple nodes sharingthe same physical optical link medium. Multicast network traffic, withthe continuous demand of more evolved distributed storage solution, hasbeen a new important concept in datacenter network traffic. Other typeof datacenter applications could also benefits from optical multicasttraffic such as, high definition media streaming and high-performancecomputing (HPC) computation synchronization.

The invention is also novel in the propose approach of being a smallform-factor pluggable (SFP) module. By daisy-chaining these opticaldevices, it is possible to convert a switch to a colorless, directionless and contention less (CDC) reconfigurable optical add-dropmultiplexer (ROADM). By using more than one of these devices within anSFP switch, it would then convert it to an optical wavelength selectionswitch (WSS) capable of transmitting a reception wavelength to the same,or another wavelength on a different switch interface. The switch canthen provide electrical power for the optical-electrical-optical (OEO)regenerator as well as inline optical amplification at both the porttransmission and port reception sides.

The ROADM architecture propose is based on multiple micro-tunablesilicon (MOTUS) optical engines such as described below in respect ofFIG. 6 and within a U.S. Provisional Patent Application 61/949,484 byFrancois Menard, Frederic Nabki and Michael Menard entitled “Methods andSystem for Wavelength Tunable Optical Components and Sub-Systems”exploiting silicon microelectromechanical systems (MEMS) and siliconphotonic circuits to provide the switching functionality within atransmitter, receiver, ROADM, etc. An overview of the silicon MEMS andsilicon photonics can be found within U.S. Provisional PatentApplication 61/949,474 entitled “Mirror Based MicroElectroMechanicalSystems and Methods” by Frederic Nabki et al. Due to the pass-throughcharacteristic of the ROADM, an amplification mechanism is proposed toachieve a cascaded ROADM transceiver topology. To compensate for theinsertion loss hit due to the complex internal optical structure of thisdevice, a post amplification process is proposed. Alternatively posttransmitter or pre-receiver amplification may be employed, the lattertypically in conjunction with a variable optical attenuator (VOA) toprevent optical detector saturation. Using the active capacity of atransceiver a quantum dot (QD) amplification is proposed and to overcomethe polarization dependent loss of such devices a dual QD amplifier withQD amplifiers on both axis so as to provide electrical to opticalamplification of the pass-through signal as well as the newly insertedsignal.

Referring to FIG. 4 there is depicted a WDM ring network 400 exploiting40 channel DWDM transmission over a single singlemode optical fiber.Accordingly, as depicted 10 leaf switches 420, Leaf·1, Leaf·2, . . . ;Leaf·10 are coupled in a ring to a single spine switch 410. At each leafswitch 420 a predetermined wavelength set is dropped and added to thesinglemode optical fiber. For example at Leaf·4 this relates toλ_(SET)(D) whilst at Leaf·8 this relates to λ_(SET)(H). Alternatively,each leaf switch 420 may contain a tunable add-drop module such asdepicted in schematic 450 in FIG. 4 comprising a tunable add-dropcircuit 460 and an optical gain block 470 to either overcome the lossesarising from the preceding fiber span and/or the tunable add-dropcircuit 460 or amplify the signal to allow for losses in the subsequentfiber span and subsequent tunable add-drop circuit 460. The inventorsrefer to the tunable add-drop module depicted in schematic 450 as aReconfigurable Optical Add/Drop Switch Transceiver with ElectronicRegeneration (ROADSTER). Accordingly, tunable add-drop/ROADSTER devicessuch as depicted in schematic 450 may be programmed at installation orsubsequently when that leaf switch 420 or other are provisioned.Equally, the characteristics may be varied during operation of theleaf-spine interconnection as depicted within FIG. 4 electronicallywithout requiring the modification of any fiber optic infrastructure orservice personnel to access the rack or bay of servers etc.

Within an embodiment of the invention using the ITU C-band grid spacingat 100 GHz and designing the system for WDM at 40 different wavelengths,e.g. channels 21 to 60, within the C-band wavelength range around 1550nm as specified by the International Telecom Union (ITU). By combining 4C-band channels at 25 Gbps in a IPPO-4 format, the full bandwidth persub-band will be 100 Gbps at each node. Accordingly each leaf switch 420may access provide up to 100 Gbps and the spine switch 410 may receivetransmit up to 1 Tbps as using this full 40 channel spectrum in theC-band it is possible to daisy chained up to 10 leaf nodes, and henceleaf switches 420, such as depicted in FIG. 4. This can be achievedusing a single ROADSTER transceiver and a single fiber strand and stillprovide 100 Gbps of bandwidth between two nodes.

Each transceiver position in the leaf is able to drop a 4 wavelengthsub-band communication channel from any other leaf that need tocommunicate with it. The selected wavelength is instantiated using acontroller that keeps track of which wavelengths are used by which leafswitch 420, and hence it's associated leaf node. The reception tuningcapacity of the ROADSTER approach allows also the establishment of oneto many node multicast network communications. A transmitted wavelengthfor multicasting is picked by the broadcasting node and those nodeswishing to receive its broadcast tune their reception wavelength to thespecified sub-band channel. Whilst this broadcast is performed othernodes can still communicate to each other using different wavelengthsusing unicast or multicast traffic.

Then as depicted in FIG. 5 an interconnection diagram 500 for multipleleaf switch rings of ROADSTER nodes, not shown for clarity, via thespine switches 410. The spine switch 410 is unnecessary unless more than10 node-to-node simultaneous communications are required on a singleROADSTER transceiver per leaf deployment. As depicted each spine switch410 comprises a spine transmitter (Tx) 510X (X=A,B,C,D) coupled to oneside of an optical cross-connect (OXC) 550 and spine receivers (Rx) 520Xcoupled to the other side of the OXC 550. The spine Tx 510X aredemultiplexed by WDM DMUX 530X and optically routed signals from the OXC550 are coupled to the spine Rx 520 via WDM MUX 540X. Accordingly, anincoming sub-band can be selected from any of the leaf-spine rings andcoupled to the same or another leaf-spine ring exploiting the ROADSTERdevices. According to the, design of the 40×40 colorless, directionless,and contentionless (CDC) OXC (10 sub-bands on 4 leaf-spine rings) pointto point routing may be implemented or multicast and point-to-point maybe supported within the same fabric.

Now referring to FIG. 6 there is depicted an architecture of a 4-channelROADSTER 600 according to an embodiment of the invention exploitingMOTUS optical engines for the extraction of 4 wavelengths, in thisembodiment, of a predefined sub-band and reinsertion of the samewavelengths with newly generated signals on the optical medium. When thefull optical band of signals is received at the ROADSTER 600 (Rx) at RxIn port 600B the signals are coupled initially via a first OpticalAmplifier 685A and an optical isolator 655 to a MOTUS basedReconfigurable Band DMUX 650 which tunes to a selectable sub-band filterand accomplishes two distinct operations. First, the selected sub-bandis dropped and secondly, the remaining channels are coupled to 2:1 MUX680 via the optical isolator 655 and therein recoupled to the networkvia Tx Out port 600A. The selected sub-band is coupled via the opticalisolator 655 to a Channel DMUX 660 wherein the discrete wavelengths inthe sub-band are separated and coupled to 4 photodetectors (PDs) devicesthus extracting the modulated optical signals into an electricalquadruple communication port programming interface (CPPI-4) at the hostlevel within controller 690.

Also depicted are four MOTUS based Lambda Tunable transmitters Tx1 610to Lambda Tunable transmitter Tx4 640 respectively which are used togenerate the new optical signals within the dropped sub-band forre-insertion into the network. The electrical CPPI-4 sub-band signalfrom a host is modulated to the right wavelengths on each MOTUS basedLambda Tunable transmitters Tx1 610 to Lambda Tunable transmitter Tx4640 respectively. Each of the Lambda Tunable transmitters Tx1 610 toLambda Tunable transmitter Tx4 640 respectively has 10 programmablewavelengths of operation such that the 10 sub-bands are supported by theappropriate selection of the distributed brag reflector (DBR), e.g.Bragg grating, within the MOTUS optical engine. Accordingly, theActuator Driver Circuit 695 aligns the silicon MEMS mirrors within thefour transmitting MOTUS optical engines to the desired sub-band.Accordingly, the tunable source comprising either a wideband laser incombination with the MOMS optical engine or an optical gain block withina resonant cavity with the MOTUS optical engine provides the appropriatewavelength from the selected sub-band which is then coupled to anexternal modulator within each of the Lambda Tunable transmitters Tx1610 to Lambda Tunable transmitter Tx4 640 respectively. The opticalsignals are then coupled to 4:1 MUX such that at this stage the fournewly generated signals are combined together to generate the newsub-band. Subsequently, and then in 2:1 MUX 680 this new sub-band is arecoupled to the remaining passed-through (non-selected) sub-bands andthen amplified with second Optical Amplifier 685B before re-launch intothe optical network.

Optionally, another ROADSTER mode of operation would be to pass-throughall sub-bands directly from the Rx In port 600B to the Tx Out port 600Avia the Optical Amplifier such that no wavelength would be dropped andno new signal would be inserted. In this scenario ROADSTER is use as anin-line amplifier only and hence may be employed within an initiallydeployed leaf-spine ring prior to the population of the leaf node withserver connections. As soon as a server connections are made to the leafnode containing the leaf switch then the leaf-spine ring network isadvised of the traffic and the ROADSTER 600 is configured. It would beevident that other configurations of the ROADSTER 600 may be employed innetworks according to embodiments of the invention such as providing fora 40-channel C-band ring in an East-West direction and a 40-channelC-band ring in a West-East direction allowing loop-back configuration inthe event of a physical infrastructure failure. Alternatively, theEast-West and/or West-East ring may be operating at L-band (1565nm≤λ≤1625 nm) rather than the C-band (1530 nm≤λ≤1565 nm). In otherembodiments other wavelength bands such as O-band (1260 nm≤λ≤1360 nm),E-band (1360 nm≤λ≤1460 nm), S-band (1460 nm≤λ≤1530 nm), and U-band (1625nm≤λ≤1675 nm), may also be employed, for example.

Optionally the Optical Amplifier 685 may be placed on the receive sideprior to the Reconfigurable Band DMUX 650 or amplification may beprovided on both the receiving and the transmitting sides, e.g. anoptical amplifier may be provided on the transmit side with anotherlower gain amplifier on the selected band demultiplexed prior to ChannelDMUX 660. In embodiments of the invention with quantum dot semiconductoroptical amplifiers (QD-SOA) placed on the receive side provide a smarteramplification process that may be employed for keeping the amplificationlinear and overcoming saturation.

An example of the channel wavelength plan for a C-band leaf-spine ringand accordingly the sub-band wavelengths for each of the Lambda Tunabletransmitters Tx1 610 to Lambda Tunable transmitter Tx4 640 respectively,λ1, λ2, λ3, λ4, and the 4 channel receiver within the Channel DMUX 660,λ1, λ2, λ3, λ4, is given in Table 1 below.

TABLE 1 Wavelength Allocation Plan according to an Embodiment of theInvention (C-Band Channel Numbers) A B C D E F G H I J λ1 21 25 29 33 3741 45 49 53 57 λ2 22 26 30 34 38 42 46 50 54 58 λ3 23 27 31 35 39 43 4751 55 59 λ4 24 28 32 36 40 44 48 52 56 60

By daisy-chaining multiple ROADSTERs in a ring topology, multipleROADSTERs can be installed in a spine switch facing the east side of thering in transmit mode and multiple ROADSTERS can be facing the west sideof the ring in receive mode. Since in a Leaf Spine Topology,leaf-to-leaf communications is always through a Spine, this ensures aLeaf Spine topology enforcement while enabling single fiber operation,allowing for all communications to occur in the DWDM C-band withoutneeding to use the L band in the reverse direction on the same fiber.Essentially, the network becomes a forward only ring with datacomoriginating from the Spine dropped along the way to multiple leaves,with signals being re-inserted on the ring by the leaves such as to senddata back to the spine by reusing the same wavelength for establishing aunicast communication channel e.g. the same transmit and receivedsub-band are tuned by both leaf switches.

FIG. 21 depicts such an architecture allowing sub-band reuse for unicastcommunication going from leaf node 2110 to spine node 2120 between twoleaf nodes 2110 within a leaf-spine network 2100 such as depicted anddescribed supra in respect of FIG. 4 and WDM ring network 400. Asdepicted the ring comprises first to tenth leaf nodes 2110, identifiedas Leaf 1, Leaf 2, . . . ; Leaf 10. Accordingly, Leaf 1 exploitssub-band A (SB-A) for transmit and receive such that if Leaf 6 alsotunes to SB-A then it will receive the optical signals from Leaf1 andtransmit on SB-A as well thereby re-using the wavelengths within SB-A.Similarly, Leaf 8 exploits sub-band B (SB-B) for transmit and receivesuch that if Leaf 3 also tunes to SB-B then it will receive the opticalsignals from Leaf 8 and transmit on SB-B as well thereby re-using thewavelengths within SB-B. Absent any routing within the spline node 2120the transmitted signals from each of Leaf 6 and Leaf 8 will wrap aroundto Leaf 1 and Leaf 3 respectively unless another preceding node is tunedto their respective sub-bands.

Initially, it may appear confusing to see direct communication betweenLeaf 1 and Leaf 6 for example as this appears to break the rule of aleaf-spine topology by using a leaf node to leaf node directcommunication but the duality of the communications involved between thetwo leaf nodes still need to go via the spine 2120 as Leaf 6 sends itsreply back to Leaf 1 through the spine 2120. Since the sub-band isreused, only half the communication bandwidth is going through the spinethereby allowing for a doubling in the total bandwidth capacitycommunication occurs between two leaf nodes within the same ring.

Referring to FIG. 22 there is depicted an interconnection diagram 2200for two ROADSTER network rings 2100 using a contention less, directionless, colorless optical switch 2210 whilst providing filter-less andcolorless SOA overlay amplification to a dual-polarization 16 aryquadrature amplitude modulation (DP-16 QAM) network via the pass-throughfunctionality of the polarization less SOA within each ROADSTER. Alsoreferring to FIG. 23 there is depicted a protected leaf-spine network onthe same ring using two different optical fibers in two independentROADSTER network rings each comprising a spine node and ten leaf nodesas depicted in FIG. 23 and as discussed supra in respect of FIGS. 4 and21. Further referring to FIG. 24 there is depicted a multicast scenariofor a leaf-spine network such as depicted in FIG. 4 according to anembodiment of the invention wherein some leaf nodes are multicast masternodes providing the wavelength(s) for multicasting and other leaf nodesare part of a multicast group associated with a multicast master suchthat they receive the wavelength(s) multicast by the multicast masternode for that multicast group.

Referring to FIG. 7 there are depicted schematics of first and secondMOTUS optical engines 700 and 750 respectively which form part of thewavelength programmable transmitters, e.g. each of the Lambda Tunabletransmitters Tx1 610 to Lambda Tunable transmitter Tx4 640 respectively,and the Reconfigurable Band DMUX 650. Details of the first and secondMOTUS optical engines 700 and 750 can be found within a US ProvisionalPatent Application by Provisional Patent Application 61/949,484 filedMar. 7, 2014 by Francois Menard, Frederic Nabki, Michaël Ménard, andMartin Berard entitled “Methods and System for Wavelength TunableOptical Components and Sub-Systems” and the associated PatentCooperation Treaty filed Mar. 9, 2015 entitled “Methods and System forWavelength Tunable Optical Components and Sub-Systems” in which theinventors describe silicon microoptoelectromechanical systems (MOEMS)and silicon photonic circuits to provide the switching functionalitywithin a transmitter, receiver, ROADM, etc. An overview of silicon MEMS,MOEMS and silicon photonics can also be found within US ProvisionalPatent Application 61/925,290 entitled “Mirror BasedMicroelectromechanical Systems and Methods” by ‘Frederic Nabki et al.and its associated Patent Cooperation Treaty PCT/CA2015/000007 filedJan. 7, 2015 entitled “Mirror Based Microelectromechanical Systems andMethods.”

As depicted first MOTUS optical engine 700 comprises an input/outputwaveguide 760 that couples through Bragg Waveguide Array & ChannelWaveguides 730 to the semi-circular mirror via a planar waveguide inSemi-Circular Shaped Mirror & Planar Waveguide 720. According, theoptical signal from the input/output waveguide 760 is reflected andcoupled to one of the distributed Bragg reflectors (DBRs) within theBragg Waveguide Array & Channel Waveguides 750. The optical signalsreflected from the selected DDR within the Bragg Waveguide Array &Channel Waveguides 750 are then reflected back through the Semi-CircularShaped Mirror & Planar Waveguide 720 to the input/output waveguide 760.Accordingly, a wideband optical signal is filtered by the appropriatelyselected DBR within the Bragg Waveguide Array & Channel Waveguides 750or a cavity formed comprising the selected DBR within the BraggWaveguide Array & Channel Waveguides 750 and an external optical gainmedium with a broadband reflector may become a wavelength settable lasersource.

Now referring to second MOMS optical engine 700 then this similarlycomprises an input/output waveguide within the Planar Lens and WaveguidePair 740 which couples through Bragg Waveguide Array & ChannelWaveguides 730 to the semi-circular mirror via a planar waveguide inSemi-Circular Shaped Mirror & Planar Waveguide 720. According, theoptical signal from the input/output waveguide 760 is reflected andcoupled to one of the distributed Bragg reflectors (DBRs) within theBragg Waveguide Array & Channel Waveguides 750. The optical signalsreflected from the selected DBR within the Bragg Waveguide Array &Channel Waveguides 750 are then reflected back through the Semi-CircularShaped Mirror & Planar Waveguide 720 to the input/output waveguide 760.Accordingly, a wideband optical signal is filtered by the appropriatelyselected DBR within the Bragg Waveguide Array & Channel Waveguides 750.However, in contrast to first MOTUS optical engine 700 rather thansignals within the optical signal coupled to the MOTUS optical enginethat are not reflected by the selected DBR within the Bragg WaveguideArray and Channel Waveguides 730 being lost these propagate through intothe Planar Lens and Waveguide Pair 740 wherein a planar lens focussesthese optical signals to a second channel waveguide within the PlanarLens and Waveguide Pair 740. Accordingly, the reflected signals from theDBR are the selected sub-band which are then coupled to the Channel DMUX660 whilst the optical signals passed through are coupled to thewaveguide and out from the second MMUS optical engine 750 and thereincoupled to the 2:1 MUX 680.

Accordingly, referring to FIG. 8 there is depicted a schematic of4-channel ROADSTER 600 as described supra in respect of FIG. 6exploiting first and second MOTUS optical engines 700 and 750respectively. Accordingly, there are depicted Lambda Tunabletransmitters Tx1 610 to Lambda Tunable transmitter Tx4 640 respectivelywhich exploit the first MOTUS optical engine 700 in conjunction with anoptical gain element 810 and external modulator 820. The outputs ofthese couple via 4:1 MUX 670 to 2:1 MUX 680 and therein to the Tx Outport 600A. The Rx In 600B signals are coupled to the Reconfigurable BandDMUX 650 via circulator 830, the Reconfigurable Band DMUX 650 comprisingsecond MOTUS optical engine 750 wherein the selected sub-band is coupledback to the circulator 830 and therein to the Channel DMUX 660. Thepassed-through sub-bands are coupled to the 2:1 MUX 680 and therein tothe Tx Out port 600. Any optical amplification within the ROADSTER 600has been omitted for clarity.

As depicted the Channel DM UX 660 is an array of Bragg grating devices,such as grating assisted reflective directional couplers or gratingassisted transmissive directional couplers for example in order toremove the requirement for isolators to separate reflected opticalsignals from the forward propagating signals. The Bragg grating devicesmay be cyclic, low free spectral range, geometries such that one ChannelDMUX 660 operates on all bands.

2: Gridless Wavelength Dependent Add/Drop with Wavelength/Spectralre-use

A new generation of optoelectronics equipment with integrated wavelengthdivision multiplexing capabilities and targeted at datacenter fabrics isnow emerging. As depicted supra in respect of FIGS. 4 and 5 leaf-spineinterconnection can be mapped to a single optical fiber with 40 channelsat 25 Gbps. Within the prior art a switch vendor has recentlyimplemented a 10 Gbps ToR switch that makes use of 2 channels of CWDM onfibers within a 12-count multi-fiber chordal ring to implement a 2:1oversubscribed 240 Gbps ring topology for rings up to 10 km made up ofup to 11 switches.

However, the inventors have established that with WDM-PON technology,the same chordal ring topology would be capable of 10× as many channelsand of much greater distances. Further, the inventors have establishedan approach to enabling multi-degree interconnection through dense WDM(DWDM), e.g. 100 GHz channel spacing, which reduces the number of fiberoptic links by passively establishing multipoint connectivity throughoptical wavelengths. In a datacenter environment, DWDM technology cantherefore be leveraged to extend spine switches all the way to thecomputing nodes, foregoing the need for ToR switches.

The inventors have established that a non-blocking any-to-anyconnectivity with latencies only made possible by full mesh connectivitydown at the physical layer becomes possible with DWDM Technology, while,keeping the number of links as a linear function of the number ofinterconnected nodes. Within the prior art WDM devices such as 80channel 50 GHz spacing cyclic athermal arrayed waveguide gratings allowthe multiplexing of 80 C-band and 80 L-band channels to provide DWDMbased transport of 160 individual wavelengths, 80 East and 80 West, on asingle strand of single mode optical fiber. With conventional modulationand direct detection at 25 Gbps per wavelength, each channel of 100 Gbpswould require 8 wavelengths (4 in the DWDM L band, 4 in the DWDM Cband). Thus, it is possible to transport (160/8)=20 channels of 100 Gbpsonto a single fiber, which equates to 2 Tbps on a single fiber.

Subsequently, without any change to the fiber optic and WDM-PONmultiplexers, the same passive infrastructure will be able to support 80channels of 100 Gbps, or 8 Tbps on a single strand of single modeoptical fiber, with higher order modulations and coherent reception.With today's WDM therefore every link can support n channels throughmultiple wavelengths where n can be up to 88 full duplex channels.Consequently, the number of wavelength paths in a protected meshtopology built over a WDM layer would remain on the order of 2n², butthe number of physical links would be exponentially reduced down to 2*nwhich is substantially lower than the 2n² within the protected meshtopology.

As depicted in FIG. 9 wherein only a portion of the deployed chordalDWDM is depicted for a node 910 within a network 900 wherein eachsubsequent node within the network is connected to the node 910 via aspecific wavelength, e.g. the first node by λ1, the second node away byλ2, etc. and then the sixteenth node by λ16 for example, etc.Accordingly, for a 32 node WDM choral ring according to an embodiment ofthe invention a partial view of the interconnections is depicted in FIG.10 with first schematic 1000 and for three fully populated nodes insecond schematic 1050.

It would be evident that in hyperscale datacenters such an architecturewill translate to significant costs savings in the cablinginfrastructure while at the same time providing the fully meshedtopology necessary to scale out of HM clouds. Further, as WDM-PONtechnology is based on low-loss dense wavelength division multiplexers,WDM-PON links can thus be used to build highly resilient fault toleranttopologies that can span multiple datacenters in the same metropolitanmarket. Further, since DWDM technology operates in the portion of thefiber optic spectrum that can be amplified, using erbium doped opticalamplifiers, the links can be tens to hundreds of kilometers such thatthe multiple datacenters can be connected across larger geographicaldistances directly without relying upon telecommunications networkinfrastructure of if designed and implemented in conjunction totelecommunications networks the wavelength signal(s) betweengeographically dispersed datacenters may be transported upon so-called“dark fiber” or be channels on a live fiber leased from atelecommunications network provider.

3. Intelligent WDM-PON Node with Remote Latching Mems and OTDR

Referring to FIG. 11A there is depicted a WDM node with a remotelatching MEMS switch and optical time domain reflectometry (OTDR) linkfault detection. As depicted the node comprises uncolored receivers 1120which receive data from remote transmitters 1110, such as for exampleLTE base stations. These received signals are then applied, where theyare to be transmitted from the WDM node, to coloured wavelengthtransmitters (e.g. C band or L band) 1130A which are coupled to C+L bandAWG 1140. The output from the C+L band AWG 1140 are coupled via OpticalProtection Latching Switch 1150 before an Optical Supervisory Channel(OSC) is overlaid through OSC overlay multiplexer 1650 and therein tothe singlemode transmission network. At the remote node the OSC signalis extracted from the incoming WDM signal and coupled to AWG Controllerand OSC Monitoring 1185. The C-band WDM signals are then coupled via anoptical switch 1155 to a remote C+L AWG 1190 and the C-band signalsrouted to remote Small Form-Factor Pluggable (SFP) transceivers 1135with ColourPlug™ filter patchcords such as described below in respect ofSection 4.

The output from the SFP transceiver 1135 in the L-band is coupled backto the C+L AWG 1190 wherein it is WDM multiplexed back to the opticalswitch 1155 and transmitted back to the node wherein the L-band WDMsignals are demultiplexed by the C+L band AWG 1140 and coupled toReceivers 1130B. Accordingly, up to 40 channel 100 GHz duplex links or80 50 GHz duplex links can be supported over a single optical fiber withC-band downstream transmission and L-band upstream transmission.

Additionally, the Optical Protection Latching Switch 1150 and opticalswitch 1155 are coupled to a second optical fiber that routes betweenthe node and remote node over a different geographic path. Opticalsupervisory overlay is also provided on this second optical fiber againfrom the node. The OSC—Embedded OTDR sources 1195 also include embeddedOTDR functionality together with the OSC signal. Accordingly, failure todetect an OSC signal at the node on the primary fiber is indicative of afailure such that the optical switch connects to the second fiber. Sucha failure would also be detected by the embedded. OTDR within the OSCsource thereby triggering a switching of the optical protecting latchingswitch 1150 which then latches into the new state. The opticalprotecting latching switch 1150 and the pair of OSC—Embedded OTDRsources 1195 are coupled to Network Operations Center 1180. Accordingly,high channel count duplex transmission can be supported between a nodeand a remote node with automatic failover protection through opticalsupervisory channel and embedded ODTR functionality.

Now referring to FIG. 11B there are depicted first and second protectionarchitectures 1100A and 1100B respectively employing micro-OTDR (μOTDR)and latching 1×2 MEMS protection switching exploiting SFP pluggablemodules and out of band communications according to embodiments of theinvention. In first protection architecture 1100A DWDM SFP+ modules11010(1) to 11010(N) are coupled to a DW DM 11050 and therein to 1×2optical protection switch (OPS) 11060 within OPS SFP 11040. From the 1×2OPS 11060 the outputs route to filter 11070 and then geographicallydiverse fibers to the remote node. The filters 11070 each couple theoutput of μOTDR SFPs 11020 and 11030 to the geographically diversefibers. At the remote node other filters 11070 remove the out of bandμOTDR signals from the DWDM signals. The active optical fiber is routedvia an 1×2 OPS 11060 to DWDM 11050 and therein to DWDM SFP+ modules11010(1) to 11010(M) within the remote node. In the event of a fiberfailure the μOTDR, e.g. μOTDR SFP 11020, detects a back reflection andtrigger the 1×2 OPS 11060 within the node to switch the DWDM signals tothe geographically diverse fiber. The 1×2 OPS 11060 within the remotenode is switched based upon the μOTDR signal on the broken fiber notbeing detected. Each 1×2 OPS 11060 employs a latching 1×2 silicon MEMSoptical switch.

Within second protection architecture 1100B the DWDM output is coupledto μOTDR-OPS SFP 11090 housing the nOTDR laser 11095, filter 11070, and1×2 OPS 11060 such that the μOTDR-OPS SFP 11090 couples to thegeographically diverse fibers. Accordingly first and second protectionarchitectures 1100A and 1100B each provide SFP modules with embeddedprotection switching and out of band control interfaces. It would beevident to one skilled in the that the 1×2 OPS 11060 may provideconnectorised interfaces for connecting the μOTDR-OPS SFP 11090 to theDWDM and the outputs of the 1×2 OPS 11060 to their optical links toremote node. Optionally, 1×2 OPS 11060 may be an 1×N OPS or a 2×N whereN≥2 allowing another out-of-band communications signal to be added inparallel to or in replacement of the optical signals from μOTDR laser11095.

4. L-BAND/C-BAND Patchcord with Embedded Silicon Optical Bench

Referring to FIG. 12 there is depicted a schematic of a bidirectionallink between a first transceiver 1220 within a Central Office 1210 and asecond transceiver 1280 within a Remote Location 1290. The firsttransceiver 1220 in this instance is L-band transmit/C-band receive andis coupled via, a first patchcord 1230 to downstream MUX 1245 andupstream DMUX 1240 the single channel outputs from the downstream MUX1245 and upstream DMUX 1240 are coupled via an L−C band coupler to C+Lcyclic AWG 1260 over a fiber optic link. The output of a channel of theC+L, cyclic AWG 1260 is coupled to second transceiver 1280 via secondpatchcord 1270. Second transceiver 1280 is a C-band transmit and L-bandreceive.

An embodiment of the transceiver end of the first patchcord 1230 isdepicted in FIG. 13 with internal partial schematic 1300 and externalassembly 1350. Accordingly, a silicon optical circuit 1320 is depictedwith two inputs and two outputs which forms part of the connectorassembly. Disposed between the lower input and output is an L-band Bragggrating such that the colourless first transceiver 1220 is now colouredin the L-band. The C-band is a pass through as it has been coloured bythe upstream DMUX 1240.

An embodiment of the transceiver end of the second patchcord 1270 isdepicted in FIG. 14 with internal partial schematic 1400 and externalassembly 1450. Accordingly, a silicon optical circuit 1420 is depictedwith one input and two outputs which forms part of the connectorassembly. The silicon optical circuit 1420 incorporates a C/L thin filmfilter (TFF) 1430 and a C-band. Bragg grating 1410. Accordingly, whenconnected to the second transceiver 1280 the C-band Bragg grating turnsthe colourless C-band source into a coloured transmitter in the C-band.The C/L TFF 1430 provides the required C/L band separation for thesecond transceiver 1280 and single fiber connectivity to the C+L cyclicAWG 1260. The L-band is a pass through as it has been coloured by theC+L cyclic AWG 1260.

Optionally, the first patchcord 1230 may include a C/L TFF 1430 and onlyhave a single optical pigtail. Additionally whilst the C/L TFF 1430 isdepicted in internal partial schematic 1400 as splitting the C- andL-bands in the forward propagating direction it would be evident to oneskilled in the art that in fact according to the design of the C/L TFF1430 either the C- or L-band would be reflected and accordingly this isaccommodated by folding/bending its optical path. To the user thisaspect is hidden.

It would be evident that alternatively to the fiber Bragg gratings thatsingle channel C and L and L band TFFs may be employed within siliconoptical circuits or a micro-optic assembly to provide the samefunctionality. It would also be evident that the concept may be expandedto allow for C+L band separation, band filtering, and single channelfiltering all within the same patchcord connector assembly wherein theconnector assembly now supports perhaps 2 or more channels and theassociated number of connections. Optionally, the assemblies such asdescribed supra in respect of FIGS. 12 to 14 may be deployed within ahousing within a patchcord or may form part of a discreteconnector-receptacle housing such that this the connector end isinserted into the receptacle of a transceiver, e.g. an SFP or SFP+transceiver, and then a standard patchcord is inserted into thereceptacle.

5. Silicon Mems based Tunable Optical Transmitters Receivers andPluggable Transceivers

Referring to FIG. 15A there is depicted a wavelength selective MOTUS1550 optical engine according to an embodiment of the invention actingas the tuning element for a wavelength selective receiver 1500.Accordingly an input optical signal is coupled to an optical circulator1510 wherein it is coupled to the MOTUS 1550. The reflected signal atthe wavelength selected by tuning the SC-MEMSM within the MOTUS 1550 isthen coupled back to the optical circulator 1510 and therein to thephotodetector 1520. Whilst the optical circulator 1510 provides forseparation of the input forward propagating signals and backwardpropagating signals these can be bulky and expensive devices. Analternate wavelength selective receiver 1500E wherein the wavelengthselective MOTUS 1550 optical engine has been replaced with wavelengthselective MOTUS 1560 wherein the mirror MOEMS element has been replacedwith a beam 1540 upon which is disposed waveguide 1530 which couples toinput/output optical waveguide 1570. Accordingly, activation of the MEMSactuator again pivots the MOEMS but now this is the beam 1540 withwaveguide 1530 rather than the MOEMS with planar waveguide and mirrorelements. The optical circulator 1510 and photodetector 1520 required toform the wavelength selective receiver 1500B with wavelength selectiveMOTUS 1560 have been omitted for clarity.

Accordingly, referring to FIG. 16A there is depicted a wavelengthselective receiver (WSR) 1600 according to an embodiment of theinvention exploiting a wavelength selective MOTUS optical engine withBragg grating based transmissive Fabry-Perot filters and couplercombiners. Accordingly the SC-MEMSM mirror allows for selection of theappropriate Fabry-Perot filter 1640 within the array of Fabry-Perotfilters. Each Fabry-Perot filter 1640 is comprised of first and secondBragg gratings 1630A and 1630B that act in conjunction with one anotherto provide a high finesse filter, see for example Legoubin et al in“Free Spectral Range Variations in Grating-Based Fabry-Perot FiltersPhotowritten in Optical Fibers” (J. Opt. Soc. Am. A, Vol. 12, No. 8,pp-1687-1694). The outputs of the upper and lower waveguide groups areeach coupled to a multi-mode interferometer (MMI), first and second MMI1610A and 1610B respectively, and therein to first and secondphotodetectors 1620A and 1620B.

Similarly, FIG. 16B depicts a selective receiver (WSR) 1650 according toan embodiment of the invention exploiting a wavelength selective MOTUSoptical engine similar to that described in respect of FIG. 15B in thata waveguide 1530 is disposed upon a beam 1540 coupled to a MEMS actuatorvia a pivot point such that the tip of the waveguide 1530 can be rotatedand aligned to the selected optical waveguide. As with FIG. 15B theinput to the WSR 1650 is via an input waveguide 1630 upon the MEMSstructure. It would be evident that the rotary MEMS actuators depictedwithin FIGS. 15B and 16B may be replaced with lateral linear and/orlateral angular MEMS actuators allowing the input waveguide to bedirectly along the beam without requiring the 90° bend.

Now referring to FIG. 17 there are depicted first and secondcross-sections X-X and Y-Y through a wavelength selective opticaltransmitter according to an embodiment of the invention incorporatingintegrated semiconductor structure 1750 comprising a semiconductoroptical gain block 1730, high reflectivity mirror 1720, and externalMach-Zehnder modulator 1710. Second cross-section Y-Y is depicted as thecross-section through the SC-MEMS and Bragg waveguide grating. Asdepicted in first cross-section X-X according to this embodiment of theinvention the semiconductor structure 1750 has been deposited directlyonto the silicon substrate of the silicon-on-insulator structure suchthe waveguide sections of the semiconductor structure 1750 arebutt-coupled to the silicon core waveguides of the MOTUS optical engine.Whilst these interfaces are depicted as being perpendicular within FIG.17 these interfaces may be angled to suppress return loss as in factthey may also be in the other embodiments of the invention in FIGS. 14and 15 for example wherein hybrid flip-chip integration is depicted.According to the operating wavelength of the MOTUS the semiconductorstructures may be AlGaInAs, InGaAsP, and GaAs based for example.

Within other embodiments of the invention according to variations offlip-chip mounting the semiconductor optical gain block and externalmodulator evanescent coupling from the passive waveguides, see forexample Park et al. in “A Hybrid AlGaInAs—Silicon Evanescent Amplifier”(IEEE Phot. Tech. Lett., Vol. 19, pp. 230-2.32) and Bowers et al. in“Integrated Optical Amplifiers on Silicon Waveguides” (Proc. IntegratedPhotonics and Nanophotonics Research and Applications, Paper ITuG1,2007).

Within other embodiments of the invention the semiconductor opticallaser may be folioed within the silicon core waveguides using conceptsincluding, but not limited to, microring lasers. At other wavelengthranges, e.g. 1300 nm, structures such as semiconductor componentscomprising a Si substrate, an active region, and a Si capping layer onsaid active region. The active region, see U.S. Pat. No. 6,403,975, maybe a superlattice comprising alternating layers of Si(1-y)C(y) andSi(1-x-y)Ge(x)C(y). In another embodiment it is a superlatticecomprising a plurality of periods of a three-layer structure comprisingSi, Si(1-y)C(y) and Si(1-x)Ge(x) and in another a plurality of periodsof a three-layer structure comprising Si, Si(1-y)C(y) andSi(1-x-y)Ge(x)C(y) layers.

FIG. 18 depicts a transceiver 1810 employing a transmitter opticalsub-assembly (TOSA) 1820 and a receiver optical sub-assembly (ROSA) 1830exploiting tunable transmitter and receiver optical engines according toembodiments of the invention described supra in exploiting MEMS mirrorelements in conjunction with wavelength selective elements. Accordingly,as depicted the transceiver 1810, e.g. an SEP transceiver, may be fittedto systems and in fact directly onto server blades etc. whilst providingtunable transmit and receive functionality rather than the standardcolourless modules currently commercially available or coloured asdiscussed supra in respect of FIG. 12 by embedded Bragg gratings/C+Lfilters into connector assemblies for example.

FIG. 19 depicts a transceiver 1910 employing a single integratedTOSA/ROSA sub-assembly 1920 wherein the TOSA and ROSA each exploittunable transmitter and receiver optical engines according toembodiments of the invention described supra in exploiting MEMS mirrorelements in conjunction with wavelength selective elements. Accordingly,as depicted the transceiver 1910, e.g. an SFP transceiver, may be fittedto systems and in fact directly onto server blades etc. whilst providingtunable transmit and receive functionality rather than the standardcolourless modules currently commercially available or coloured asdiscussed supra in respect of FIG. 12 by embedded Bragg gratings/C+Lfilters into connector assemblies for example.

FIG. 20 depicts a transceiver 2010 employing a single integratedTOSA/ROSA sub-assembly 2020 wherein the TOSA 2020A and ROSA 2020B eachexploit tunable transmitter and receiver optical engines according toembodiments of the invention described supra in exploiting MEMS mirrorelements in conjunction with wavelength selective elements. Additionallythe single integrated. TOSA/ROSA sub-assembly 2020 incorporates a C+Lfilter 2020C such that the transceiver 2010 may be C-band receive andL-band transmit for example or L-band receive and C-band transmit. Itwould be evident that in other embodiments of the invention the TOSA2020A and ROSA 2020B may contain wavelength selective elements that areboth C and L band. In this instance, the C+L filter 2020C may bereplaced with a compact optical isolator. Similarly, such an opticalisolator may be employed with the single integrated TOSA/ROSAsub-assembly 1920 within the transceiver 1910 of FIG. 19 to providesingle fiber operation or with the TOSA 1820 and ROSA 1830 oftransceiver 1810 in FIG. 18 for similar single fiber operation. Theoptical isolator may be a compact free-space design such as known in theart or a monolithically integrated isolator.

6. Silicon Mems Based Optical Switch Matrices

Now referring to FIGS. 25 and 26 there are depicted 4×4 and 8×8 opticalswitch matrices according to embodiments of the invention employing andMMUS optical engines respectively in conjunction with directionalcoupler based routing to the optical receivers. Within FIG. 25 a 4×4optical switch 2500 comprises first to fourth MOTUS optical engines2510A to 2510D which are coupled to data sources, not shown for clarity,and select an output port for transmission to a selected receiver offirst to fourth optical receivers 2520A to 2520D respectively undercontrol of a controller, not shown for clarity. Each output port from aMOTUS optical engine 2510A to 2510D respectively is coupled via one ormore directional couplers to the selected receiver. Due to the design ofthe cross-over matrix each optical path consists of horizontal andvertical links to f from the directional couplers such that opticalcross-overs between paths are 90 degrees for high crosstalk and lowloss. However, the architecture also reduces the number ofcross-connects when compared to a conventional fully connectedarchitecture.

In contrast, in FIG. 26 an extension of the design methodology ispresented for switch matrix wherein first to eighth pluggabletransceivers 2610A to 2610H are coupled to first to eighth MOTUS opticalswitches 2620A to 2620H and first to eighth receivers 2630A to 2630Hrespectively. The optical output of each first to eighth MOTUS opticalswitches 2620A to 2620H is coupled to a directional coupler basedrouting matrix and therein to the appropriate receiver of the first toeighth receivers 2630A to 2630H respectively. This configurationprovides for loop-back whereas if this feature is not required thematrix can be reduced to a multiple fiber interconnect. Again due to thedesign of the cross-over matrix each optical path consists of horizontaland vertical links from each MOTUS optical switch to a receiver via thedirectional couplers such that optical cross-overs between paths are 90degrees for high crosstalk and low loss. Again, the architecture alsoreduces the number of cross-connects when compared to a conventionalfully connected architecture.

Referring to FIG. 27 there is depicted a cross-over 2700 according to anembodiment of the invention such as implemented within 4×4 opticalswitch 2500. At the cross-over 2700 each optical waveguide 2710 has ataper 2720 expanding the optical beam thereby improving the performanceof the cross-over 2700. Within the tapers 2720 sub-wavelengthnanostructures may be formed to further improve the performance of thecross-over by enhancing mode conversion to an expanded beam.Accordingly, insertion loss may be reduced.

Within the embodiments of the invention described supra in respect oftunable WDM transmitters, WDM receivers, ROADMs, ROADSTERs, WSS, etc.the devices have been described based upon tunable MEMS mirrorsoperating in conjunction with Bragg gratings to provide multiple channeltunability. Accordingly, the embodiments of the invention exploit whatthe inventors call a MOTUS optical engine. Accordingly, these devicesallow for gridless OADMs, ROADMS, WSS etc. as currently described.

Considering the ROADSTER described in respect of FIGS. 6 and 8 it wouldbe evident that the centre wavelength of the Bragg gratings may bethermally and/or mechanically tuned to offset their grids such that theysit on a predetermined grid or are offset by 50 GHz. Alternatively, asthe MOTUS optical engine may support according to its design coupling toa larger number of waveguides then potentially a MOTUS optical enginemay be implemented with say 2 CWDM gratings, 5×200 GHz gratings, 10×100GHz gratings, and 20×50 GHz gratings (or 10×50 GHz gratings with thermaland/or mechanical tuning). In this manner a MOTUS optical engine maysupport gridless networks as it is only when installed and programmedthat the device is configured as being a 200 GHz device, 50 GHz device,or even a CWDM or 100 GHz device. Within other embodiments of the MOTUSthe planar waveguide Bragg structures and MOEMS mirror may be replacedwith a MOEMS incorporating an echelle or echelon grating, for example,such that direct filtering is implemented within the MOEMS inconjunction with the input and 1 or output waveguides. Such MOTUSstructures would be truly gridless by virtue of providing continuouswavelength filtering across their designed range.

In other embodiments of the invention for example 10 C-band 100 GHzgratings may be provided together with 10 L-band 100 GHz gratings inorder to provide C or L band operation or even devices that can operateacross both in networks exploiting concurrent unidirectional C and Lband transmission rather than the more common C band in one directionand L band in the other. Equally, non-standard wavelength grid patternsmay be implemented.

Specific details are given in the above description to provide athorough understanding of the embodiments. However, it is understoodthat the embodiments may be practiced without these specific details.For example, circuits may be shown in block diagrams in order not toobscure the embodiments in unnecessary detail. In other instances,well-known circuits, processes, algorithms, structures, and techniquesmay be shown without unnecessary detail in order to avoid obscuring theembodiments.

The foregoing disclosure of the exemplary embodiments of the presentinvention has been presented for purposes of illustration anddescription. It is not intended to be exhaustive or to limit theinvention to the precise forms disclosed. Many variations andmodifications of the embodiments described herein will be apparent toone of ordinary skill in the art in light of the above disclosure. Thescope of the invention is to be defined only by the claims appendedhereto, and by their equivalents.

Further, in describing representative embodiments of the presentinvention, the specification may have presented the method and/orprocess of the present invention as a particular sequence of steps.However, to the extent that the method or process does not rely on theparticular order of steps set forth herein, the method or process shouldnot be limited to the particular sequence of steps described. As one ofordinary skill in the art would appreciate, other sequences of steps maybe possible. Therefore, the particular order of the steps set forth inthe specification should not be construed as limitations on the claims.In addition, the claims directed to the method and/or process of thepresent invention should not be limited to the performance of theirsteps in the order written, and one skilled in the art can readilyappreciate that the sequences may be varied and still remain within thespirit and scope of the present invention.

What is claimed is:
 1. A system comprising: a local node comprising: amicroelectromechanical systems (MEMS) based latching 1×N optical switchemploying a microoptoelectromechanical (MOEMS) element; M opticalsources, each optical source operating within a predetermined wavelengthrange; an optical time domain reflectometry (OTDR) generator forgenerating an OTDR signal, receiving the OTDR signal as reflected by anoptical link to which the OTDR signal is coupled and analyzing thereflected OTDR signal; N or M first optical couplers, each first opticalcoupler to couple the OTDR signal to and from a predetermined output ofthe N outputs of the MEMS based latching 1×N optical switch and thereineach optical link of N optical links from the local node; and acontroller for determining whether to change a state of the MEMS basedlatching 1×N optical switch in dependence upon at least the N OTDRsignals; and a remote node comprising: a second MEMS based latching 1×Noptical switch; R second optical couplers, each second optical couplerfor extracting an optical supervisory signal (OSC) from each opticallink of N optical links; R optical detectors, each optical detectorcoupled to a predetermined optical coupler of the R optical couplers;and a controller for determining whether to change the state of thesecond MEMS based latching 1×N optical switch in dependence upon atleast the optical supervisory signals from the R optical detectors;wherein the local node further comprises: an OSC generator forgenerating the OSC signal; N or M third optical couplers, each thirdoptical coupler to couple the OSC signal to a predetermined output ofthe N outputs of the MEMS based latching 1×N optical switch and thereineach optical link of N optical links; N is a positive integer and N≥2; Mis a positive integer and M≥2; and R is a positive integer and R=N. 2.The system according to claim 1, further comprising; a remote nodecomprising: a second MEMS based latching 1×N optical switch; R secondoptical couplers, each second optical coupler for extracting an opticalsupervisory signal from each optical link of N optical links; R opticaldetectors, each optical detector coupled to a predetermined opticalcoupler of the R second optical couplers; and a controller fordetermining whether to change the state of the second MEMS basedlatching 1×N optical switch in dependence upon optical supervisorysignals from the R optical detectors; wherein the optical supervisorysignal is the OTDR signal coupled to each optical link of the N opticallinks.
 3. The system according to claim 1, further comprising an OSCgenerator for generating an OSC signal; and N or M third opticalcouplers, each third optical coupler to couple the OSC signal to apredetermined output of the N outputs of the MEMS based latching 1×Noptical switch and therein each optical link of N optical links.
 4. Thesystem according to claim 1, wherein the MEMS based latching 1×N opticalswitch is part of a MEMS based latching 2×N optical switch; a firstinput port is coupled to one or more optical sources generating opticalsignals to be routed by the MEMS based latching 1×N optical switch; anda second input port of the MEMS based latching 2×N optical switch iscoupled to a second optical source for generating at least one of anoptical probe signal, an optical time domain reflectometry signal and anout of band communications signal; and the out of band communicationssignal is at a wavelength or wavelengths not overlapping withwavelengths of the one or more optical sources coupled to the firstinput port of the MEMS based latching 1×N optical switch.
 5. A systemcomprising: a local node comprising: a microelectromechanical systems(MEMS) based latching 1×N optical switch employing amicrooptoelectromechanical (MOEMS) element; M optical sources, eachoptical source operating within a predetermined wavelength range; anoptical time domain reflectometry (OTDR) generator for generating anOTDR signal, receiving the OTDR signal as reflected by an optical linkto which the OTDR signal is coupled and analyzing the reflected OTDRsignal; N or M first optical couplers, each first optical coupler tocouple the OTDR signal to and from a predetermined output of the Noutputs of the MEMS based latching 1×N optical switch and therein eachoptical link of N optical links from the local node; and a controllerfor determining whether to change a state of the MEMS based latching 1×Noptical switch in dependence upon at least the N OTDR signals; and aremote node comprising: a second MEMS based latching 1×N optical switch;R second optical couplers, each second optical coupler for extracting anoptical signal from each optical link of N optical links; R opticaldetectors, each optical detector coupled to a predetermined opticalcoupler of the N optical couplers; and a controller for determiningwhether to change the state of the second MEMS based latching 1×Noptical switch in dependence upon at least the optical signals from theR optical detectors; wherein the local node further comprises: anoptical supervisory signal (OSC) generator for generating an OSC signal;and N or M third optical couplers, each third optical coupler to couplethe OSC signal to a predetermined output of the N outputs of the MEMSbased latching 1×N optical switch and therein each optical link of Noptical links; and each optical signal of the optical signals from the Noptical detectors is at least one of the OSC signal and the OTDR signal.